Mirror, process of making same, and composition of reflecting element therefor



Jan. 19, 1937. w, EDWARDS 2,067,907

MIRROR, PROCESS OF MAKING SAME, AND COMPOSITION OF REFLECTING ELEMENTTHEREFOR Filed May 1, 1933 Patented Jan. 19, 1937 UNITED STATES PATENTOFFICE MIRROR, PROCESS COMPOSITION OF THEREFOR OF MAKING SAME, ANDREFLECTING ELEMENT Application May 1, 1933, Serial No. 668,805

7 Claims.

The primary object of this invention is the production of a mirrorsurface having a maximum and uniformity of substantially perfectrefiection throughout the spectrum, thus enhancing the efficiency ofvarious reflecting instruments to which my invention is applicable. Afurther object is to provide a medium of reflection which produces awhiter light because of the larger amount of blue light reflected thanheretofore. The whiter light reflected is of great importancephotographically because of the fact that films are much more sensitiveto blue than red light rays. Among further objects is the production ofa reflecting surface composed of hard and substantially untarnishablereflecting material, thus prolonging its life and efilciency. In seekingto produce a more perfect reflecting surface I have discovered a newalloy of certain metals which when properly applied to a surface of asuitable entity, serves to reflect a higher percentage and uniformamounts of light throughout the spectrum than any known medium, thusproducing a reflecting surface which is capable of greater and moreperfect reflecting power than produced. This alloy consists ofsubstantially ninety seven percent of aluminum and three percent ofmagnesium. These proportions may be varied to produce less or betterreflecting results Within the spirit of my invention.

In preparing the alloy the two proportions of metals as stated aremelted together at a temperature of substantially seven hundred degreescentigrade. During this process the metals absorb gas, which must beremoved. To accomplish this purpose the alloy is heat treated. Aftercooling the alloy is ready for use.

The accompanying drawing forming part of this specification, illustratesmy invention diagrammatically, in which Fig. 1 is a verticallongitudinal central section of the vacuum chamber in which the plate orbody of glass or other suitable material is shown placed as when havingits reflecting surface subjected to the process of condensing myimproved alloy thereon; Fig. 2 is a section taken on line 2--2 of Fig.1; Fig. 3 is a side elevation of the heater coil with my improved. alloyin place to be condensed upon the mirror body; and Fig. 4 is an enlargedsection of one form of my improved mirror or refiector.

The apparatus for the preparation of my improved reflector surfaceconsists of a housing A made of any suitable material and may resemble2. steel cylinder and be termed a vacuum chamber. This cylinder has apair of end walls l0 and l l which are removably secured to seal thecylinder ends. In this cylinder the mirror body B to be treated and anyother appurtenances may be placed. Said chamber is connected by the tubeC to suitable vacuum pumps (not shown) or other suitable air exhaustmeans for the purpose of reducing air pressure. These pumps must be veryfast and capable of producing a vacuum in the chamber of about 10* mm.pressure or better.

A heating element D composed of a spiral of preferably tungsten wire isenclosed in the lower portion of the vacuum chamber and is connected bysealed in leads E and F so that a suitable electric current may bepassed through the spiral to heat the latter. A small piece of myimproved alloy G is placed in the spiral and the temperature of theheating element raised sufficiently to vaporize said alloy in the vacuumchamber. The temperature of the heating element is raised slowly so thatany absorbed gases in the alloy will be expelled. The construction ofheating element described can be varied, any form which will vaporize myimproved alloy being contemplated within the scope of my invention.

For the purpose of cleaning the surface of the mirror body of residualgases which might effect the condensation of the vapor from my improvedalloy thereon, the mirror body B is supported in the field of anelectrical discharge between the positive electrode 1, immediately aboveand adjacent to the mirror body and the negative electrode J, locateddirectly below in the lower portion of the vacuum chamber. Theseelectrodes are suitably insulated from the cylinder wall of the vacuumchamber to protect against short circuiting and leakage from the circuitof high tension direct current with which said electrodes are connected.In practice I have used two thousand volts pressure but this may bevaried to suit requirements. The electrical discharge in the vacuumchamber between the negative electrode below and the positive electrodeabove serves to subject the lower surface of the reflector body to abombardment which cleans the surface of said body so that vapor from thealloy will condense-more evenly upon and tenaciously adhere to saidsurface, thus assisting in producing a more perfect, uniform, durableand serviceable refiecting surface.

In carrying my improved method into practice, the mirror body of anysuitable form or material is secured in place in the vacuum chamberbelow the upper electrode I by the supports H. A body of my improvedalloy to be used is placed in the heating coil D and the vacuum chamberclosed and sealed. Air pressure in the vacuum chamber is reduced toabout .02 mm. of mercury or less. Next the surface of the mirror body,such as B is subjected to bombardment by the discharge of electricitybetween the electrodes I and J to thoroughly clean the mirror surfaceand remove any residual gases. The pressure in the chamher is thenreduced to .0001 mm. of mercury and metal vapor from the alloy in theheater coil is generated by operating the heater, while the vacuumchamber is maintained at said reduced pressure. The vapor thus producedcondenses substantially uniformly over the surface of the mirror body tothe desired thickness of deposit, whereupon the operation is completedand the vacuum chamber opened and the mirror body removed. In Fig. 4 themirror body B is shown with the reflecting deposit K of my improvedalloy thereon. Said body may be composed of any substance desired suchas glass, crystal, metal or any other entity. During operation theevaporated metal radiates in direct lines from the heating element D andproduces a substantially uniform deposit on the mirror body B, providedthe pressure in the vacuum chamber is reduced sufficiently low. Toenhance uniform deposit of the metal vapor upon a surface of large areaas many heating elements and accompanying bodies of alloy may beemployed as desired to produce effective results.

In accordance with the patent statutes, 1 have described the principlesof operation of my invention, together with the composition employed,the method involved and apparatus by which the method can be carriedinto practice, but I desire to have it understood that the disclosure isonly illustrative and that modifications thereof are contemplated withinthe spirit of the invention. I do not therefore wish to be understood asconfining myself to the specific disclosure set forth, within the scopeof the following claims.

Having described my invention, what I claim as new and desire to secureby Letters Patent is:

1. The method of producing a mirror, including exposing an entity suchas a reflector body in a vacuum chamber, subjecting the surface of saidbody to the action of an electrical discharge while exposed in saidchamber, and then condensing vapor from an alloy of aluminum andmagnesium on said exposed surface in said chamber.

2. The method of producing a mirror, including exposing an entity suchas a reflector body in a vacuum chamber, subjecting the surface of saidbody to the action of an electrical discharge while exposed in saidchamber, and then condensing vapor from aluminum and-magnesium on saidexposed surface in said chamber.

3. The method of producing a reflecting surface on a reflector body,consisting of first exposing said surface in of subjecting the surfaceof said reflector body to the action of an electrical bombardment toclean said surface at a suitable vacuum pressure, and finally ofvaporizing aluminum and magnesium in said chamber and condensing saidvapor upon the surface of said body at a suitable vacuum pressure.

4. The method of producing a mirror, consising of exposing a body in avacuum chamber, of subjecting the surface of said body to the directaction of an electrical discharge while exposed in said chamber, andfinally of condensing vapor from ametallic alloy on said exposed surfacein said chamber.

5. The method of producing'a mirror, consisting of exposing a body in avacuum chamber, of subjecting a surface of said body to the directaction of an electrical discharge while exposed in said chambenandfinally of forming a reflector surface of metal on said exposed surfacein said chamber.

6. The method of producing a mirror, consist- III a vacuum chamber,second ing of exposing a body in a vacuum chamber, of

subjecting a surface of said body to the direct action of an electricaldischarge while exposed in said chamber, and finally of condensing vaporfrom a substantially pure alloy on said exposed surface in said chamber.

'7. The method of producing a mirror consisting of exposing a body in avacuum chamber, of subjecting a surface of said body to the directaction of an electrical discharge while exposed in said chamber, andfinally of condensing vapor from an aluminum alloy upon said exposedsurface in said chamber.

'HIRAM W. EDWARDS.

